Development technique for silver halide direct positive with n-vinyl-2-pyrrolidone polymer

ABSTRACT

A light-sensitive photographic material comprising a direct positive silver halide emulsion of the Herschel type containing an N-vinyl-2-pyrrolidone polymer and the development of this emulsion is described. These emulsions yield a marked increase in gradation.

United States Patent [72 Inventors Joseph Louis De Munck Kalmthout; Raymond Leopold Florens, Edegem, both of Belgium [21] App]. No. 668,685

[22] Filed Sept. 18, 1967 [45] Patented Oct. 26, 1971 [73] Assignee Gevaert-AGF A N.V.

Mortsel, Belgium [32] Priority Sept. 19,-1966 [33] Great Britain [54] DEVELOPMENT TECHNIQUE FOR SILVER HALIDE DIRECT POSITIVE WITH N-VINYL-Z- [51] Int. Cl G03c 5/24 851,774 10/1960 GreatBritain Primary Examiner-Norman G. Torchin Assistant Examiner-John L. Goodrow Attorneys-Robert F. Conrad and Alfred W. Breiner ABSTRACT: A light-sensitive photographic material comprising a direct positive silver halide emulsion of the Herschel type containing an N-vinyl-2-pyrrolidone polymer and the development of this emulsion is described. These emulsions yield a marked increase in gradation.

DEVELOPMENT TECHNIQUE FOR SILVER HALIDE DIRECT POSITIVE WITH N-VINYL-Z-PYRROLIDONE POLYMER This invention relates to an improved technique for developing light-sensitive silver halide materials.

It is known that the development of continuous tone images by means of a hydroquinone/p-N-methylaminophenol developer is accelerated under the influence of polyoxyalkalene compounds having a molecular weight preferably above 1,500. When, however, such polyoxyalkylene compounds are used in combination with a forrnaldehydebisulphite/hydroquinone developer, as known from the German Pat. application 1,141,531 filed Jan. 24, 1962 by Perutz Photowerke, an increase of the gradation together with a restrainment of the development rate is obtained. The latter developer combination is found to be very suitable for the development of light-sensitive silver halide materials suitable for use in the graphic art on account of the very contrast development obtained therewith. As light-sensitive materials for the reproduction of graphic line or screen images, socalled lith-emulsions of the silver chloride, silver chlorobromide or silver chlorobromoiodide type (normally less than 1 mole percent iodide) are generally employed.

1t has been found now that interesting sensitometric effects can be obtained by developing a direct-positive emulsion,

preferably a direct-positive emulsion showing the Herschel effect, in the presence of a N-vinyl-2-pyrrolidone polymer.

lt-has more particularly been found now that silver image with improved contrast can be obtained owing to an increase in gradation by developing, especially with a lith"-type developer, silver halide emulsions of the direct-positive type, particularly direct-positive silver halide emulsions of the lith" -type, in the presence of a combination of a polymer containing alkylene oxide units and a N-vinyl-2-pyrrolidone polymer including the latter polymer complexed with iodine. The complex is an addition complex (addition by inclusion), of molecular iodine with the N-vinyl-2-pyrrolidone polymer.

By a lith"-type developer is understood an aqueous developing solution containing as sole developing substance hydroquinone and as antioxidant a bisulphite addition compound of an aliphatic aldehyde or ketone, e.g. formaldehyde bisulphite.

It has not been possible to detect any chemical interaction between the N-vinyl-2-pyrrolidone polymer and the polymer containing oxyalkylene units so that it appears that said compounds exhibit a synergetic activity. According to a preferred embodiment of the present invention silver halide emulsions of the direct positive type suitable for the copying of line work are used in the lith development technique. Thus, it has been observed that development of such emulsions yields a marked increase of the gradation in the straight line part as well as in the toe of the density versus log l.t. curve, especially when use is made of a direct positive emulsion of the silver chloride type (iodide content less than 1 mole percent showing the Herschel effect.

In practice the improvement is particularly interesting when the direct positive photograhic material has to be reflectographically exposed, i.e., when the emulsion layer is placed in contact with the original and the photographic material is exposed through its transparent backing, which is provided with a yellow filter layer (i.e., a layer transmitting yellow light acting at the same time as antihalation layer). The areas of the direct-positive emulsion corresponding with the light-absorbing image markings of the original, possess after development a high density while the areas corresponding with the lightreflecting areas of the original have a very low density.

The material is the better suitable for reflectographic exposure the greater difference is obtained after development between the density of the image areas and that of the nonimage areas, the density of the areas of the copy corresponding with the areas of the original being preferably not greater than 0.1.

According to the Herschel effect latent image fading can be obtained by an exposure to red or infrared light. The sensitive layer is first fogged uniformly to its maximum density, e.g., with blue-violet light or by chemical means such as reducing agents, e.g., with formaldehyde or the silane compounds described in the United Kingdom Pat. specification 821,251 filed June 7, 1956 by Gevaert Photo-Producten N .V., and is image-wise exposed, e.g., behind a positive transparency, with light of a wavelength greater than 600 nm., preferably at low intensity and for a long time. If the photographic material is treated with a so-called desensitizing dye", the Herschel effect may be obtained with light of a shorter wavelength such as yellow light.

1t was not obvious that po1y(N-vinyl-2-pyrrolidone) would retard the development in a hydroquinone-formaldehyde bisulphite developer since from the United Kingdom Pat. specification 851,774 filed Sept. 17, 1958 by Agfa AG py(N- vinyl-2-pyrrolidone) was known to increase the speed when used alone in photographic emulsions developed in a N- methyl-p-N-hydroxyphenyl ammonium sulphate/hydroquinone developer,

The term N-vinyl-2-pyrrolidone polymer" when used in the present invention includes the homopolymer and copolymers of N-viny1-2-pyrrolidone as well as their iodine complexes. The N-viny1-2-pyrro1idone polymers may be of high as well as of low molecular weight, however, a molecular weight between 300 and 90,000 being preferred.

Poly(N-vinyl-2-pyrrolidone) suitable for use in the present invention is marketed, e.g., under the trade name LUVlSKOL by Badische Anilin & Soda-Fabrik, Ludwigshafen, W. Germany, and under the name of PVP, type NP (=nonpharmaceutical) by General Aniline & Film Corporation, New York, N.Y. U.S.A. The said polymer is available in viscosities of K-20, K-30, K-40 and 90.

As copolymers of N-vinyl-Z -pyrrolidone are used those of the water-soluble type and containing preferably at least 50 moles percent of N-vinyl-2-pyrrolidone units. Examples of such copolymers are copoly(vinyl acetate/N-vinyl-Z-pyrrolidone) (30/70), and copoly(sodium acrylate/N-vinyl-2-pyrrolidone) (45/55). It is self-explanatory that for obtaining a result equal to that obtained with the homopolymer a greater amount of copolymer has to be used.

Examples of suitable polymers containing alkylene oxide units are those derived from ethylene oxide and mixtures of ethylene oxide and propylene oxide or butylene oxide with the proviso that said compounds are soluble in water or an alkaline aqueous solution such as an alkaline developing bath. Preferably water-soluble polymers containing alkylene oxide units and having a molecular weight of at least 1 ,500 are used.

The preparation of alkylene glycol polymers, known as polyalkylene glycols, is described e.g. by Ellis, The Chemistry of Synthetic Resins (1935) pages 990 to 994. See therefore also the US. Pat. specifications No. 1,970,578 filed Nov. 24, 1931 by C. Scholler and U. Wittwer, 2,240,472 of Donald R. Swan, issued Apr. 29, 1941 and 2,423,549 of Ralph Kingsley Blake, Willian Alexander Stanton and Ferdinand Schulze, issued July 8, 1947. Their use as sensitizers for silver halide emulsions is described in the United Kingdom Pat. specification 600,058 filed Jan. 10, 1945 by duPont de Nemours and US. Pat. specification 2,441,389 of Ralph Kingsley Blake, issued May 11, 1948 Further examples are the condensation products of alkylene oxides with organic compounds, which contain an active hydrogen atom and are soluble in the alkaline developing bath. In this respect reference can be made to the United Kingdom Pat. specifications 871,801 filed Nov. 30, 1956 by Kodak and 991,608 filed June 14, 1961 by Kodak and to the German Pat. specification 1,188,439 filed May 16, 1964 by Fuji Shashin Film.

Still further examples are the polymeric compounds containing oxyalkylene units as described in the United Kingdom Pat. specifications 920,637 filed May 7, 1959, 945,340 filed Oct. 23, 1961, and filed Nov. 2, 1961, 940,051 filed Nov. 1, 1961 and 1,015,023 filed Dec. 24, 1962 all by Gevaert Photoproducten N.V., in the US. Pat. specification 3,307,948 of Robrecht J. Thiers, Jozef F. Willems, Raymond L. Florens, issued March 7, 1967 in our published Dutch Pat. applications 6,709,016 filed June 28, 1967 and 6,612,597 filed Sept. 7, 1966, in the published German Pat. application 1,141,531 filed Jan. 24, 1962 by Perutz Photowerke, as well as the products containing amino-alkylene and oxyalkylene units described in our published Dutch Pat. application 6,614,230 filed Oct. 10, 1966 and Canadian Pat. application 997,458 filed Aug. 9, 1967 The N-vinyl-2 pyrrolidone polymer of use according to the present invention is preferably incorporated into the light-sensitive emulsion layer but may also be incorporated into a water-permeable layer under or on top of the emulsion layer, which water-permeable layer stands in water-permeable relationship with the emulsion layer.

Preferably the N-vinyl-2-pyrrolidone polymer is added to the direct-positive light-sensitive silver halide emulsion for the graphic art in dissolved form in water or a mixture of water and water-miscible organic solvents, which do not impair the photographic characteristics of the emulsion.

However, the said polymer can also be incorporated into the emulsion by imbibition, so by treating the emulsion layer with a solution containing the polymer.

The N-vinyl-Z -pyrrolidone polymer used according to the present invention can be added to the light-sensitive silver halide emulsion during different preparation steps of the lightsensitive material. Preferably, however, it is added to the emulsion just before or after the fogging step in the preparation of the direct positive emulsion.

The optimum amount of the N-vinyl-2-pyrrolidone polymer to be added to the emulsion depends on the nature of the colloid binder of the silver halide grains, on the amount and type of silver halide in the emulsion, and the stage of addition, since, when adding the N-vinyl-a-pyrrolidone polymer before washing of the emulsion, relatively greater amounts are required.

In general N-vinyl-Z-pyrrolidone polymer may be present in the light-sensitive material in an amount of mg. to 14 g. per mole of silver halide, but for best results it is preferably present therein in an amount of 10 mg. to 1 g. per mole of silver halide.

When present in the developing bath, the N-vinyl-2-pyrrolidone polymer is preferably contained therein in an amount of 10 mg. to 10 g. per litre.

When the polymer containing oxyalkylene units is used in the emulsion layer it is preferably incorporated therein in an amount ranging from 10 mg. to 10 g. per mole of silver halide. in the developing bath the polymer containing alkylene oxide units is preferably used in dissolved state in an amount of 0.1 to 10 g. per litre.

The aliphatic aldehyde or ketone bisulphite/hydroquinone developer may further comprise the usual ingredients for a socalled lith-developer" such as potassium bromide and alkaliborates and carbonates such as sodium carbonate.

The reversal speed of direct-positive emulsions for use according to the Herschel effect, has been increased by a type of dyes which in silver halide emulsions of the negative type act as desensitizers and therefore are called desensitizing dyes (see, e.g. C. E. Kenneth Mees, The Theory of the Photographic Process, Revised Edition 1954 -The MacMillan Company, New York, p. 263). In that connection reference is particularly made to desensitizing dyes of the nitrostyryl and nitrobenzylidene type, representatives of which are described, e.g., in the United Kingdom Pat. specifications 667,206 filed June 28, 1949 by Kodak 698,576 filed Aug. 1, 1951 and 834,839 filed May 27, 1957 both by llford. Desensitizing dyes" for use in direct-positive emulsions whereby the reversal of the image occurs in the short wavelength region of the spectrum are described, e.g., in the United Kingdom Pat. specifications 821,251 filed June 7, 1956 by Gevaert Photo-Producten N.V. and 796,873 filed Dec. 10, 1954 by Gevaert Photo- Producten N.V.

Other ingredients such as hardening agents, wetting agents,

hydrophilic colloids, latices and plasticizers, can be incorporated into the emulsion in the usual way.

The following example illustrated the present invention.

EXAMPLE A washed gelatino-silver chloroiodide (99.65 mole percent of chloride and 0.35 mole percent of iodide) emulsion was melted by heating to 50 C. and the pH was adjusted to 7 by means of sodium hydroxide. Per kilogram of emulsion were added 20 cc. of a 4 percent aqueous formaldehyde solution and 100 cc. of a 0.1 percent aqueous solution of sodium hydroxide The emulsion was kept at 50 C. for 50 min. Thereafter the pH was reduced to 6 by means of an aqueous solution of hydrogen chloride, whereupon 200 mg. of the desensitizing compound l-(2,4-dinitroanilino)-l,4-dihydro- 4,4,6-trimethyl-2-pyrimidine-thiol, the preparation of which is described in example 2 of the United Kingdom Pat. specification 796,873 filed Dec. 10, 1954 by Gevaert Photo-producten N.V., were incorporated into the emulsion.

After addition of the necessary coating aids such as a wetting agent, the emulsion was divided into portions A and B to one of which (portion 8) 100 mg. of LUVlSKOL-K were added per kg. of emulsion, said emulsion containing per kg. an amount of silver halide equivalent to 40 g. of silver nitrate LU- LUVlSKOL-K30 were added per kg. of emulsion, said emulsion containing per kg. an amount of silver halide equivalent I to 40 g. of silver nitrate (LUVlSKOL is a registered trade mark for a poly(N-vinyl-pyrrolidone) marketed by Badische Anilin- & Soda- Fabrik, Ludwigsharen, W. Germany).

The respective emulsion portions were coated in the same way on a polyester base and dried.

Both light-sensitive materials were exposed reflectographically through a gray wedge with constant 0.03 and a yellow filter layer applied to the back of the polyester base. During the exposure the emulsion layers stand in contact with an original containing white and black areas. The exposed materials were developed at 21 C. for seconds in a developing bath having the following composition:

hydroquinone 13 g. formaldehyde bisulphite 50 g. anhydrous sodium carbonate 60 g. potassium bromide 1.5 g. the oxyethylene units containing polycondcnsation product.

prepared as described in preparation 2 of the United Kingdom Patent Specification 920,637 filed May 7, 1959 by Gevaert Photo-Productcn N.V. 0.5 g. sodium bicarbonate to bring the pH to 10 water till 1,000 cc.

The sensitometric results after normal storage, and storage of the materials for 36 hours at 57 C. in an atmosphere of 34 percent of relative humidity (RH) are listed in table 1.

The total speed (S) is expressed in percent with respect to the reference emulsion, the total speed of which is arbitrarily given the value 100.

The difference in density in the developed copying materials A and B between the areas corresponding respectively with the white and black areas of the original is listed in table 1 in the column designated by AD.

Two gamma-values are given Viz. the gamma in the toe of the sensitometric curve (yr) and the gamma in the straight line part of that curve (7s). The gamma in the toe of the curve was determined between the density values 0.1 and l of the densi- When using lg. of copoly(N-vinyl-Z-pyrrolidone/ammonium maleinate) (50/50) instead of 100 mg. of LUVISKOL K30 per kg. of emulsion, the AD value obtained in the same processing conditions was also higher than 3.5

l. A light-sensitive photographic material comprising a direct positive overall prefogged silver chloride emulsion layer containing less than one percent iodine and containing a polymer of N-vinyl-2 pyrrolidone, said material exhibiting the Herschel effect.

2. A light-sensitive photographic material according to claim 1, wherein the emulsion layer is a direct positive silver halide emulsion layer of the lith type.

3. A light-sensitive photographic material according to claim 1, wherein the emulsion layer contains a polymer containing alkylene oxide units.

4. A light-sensitive photographic material according to claim 2, wherein the emulsion layer contains the N-vinyl-2 pyrrolidone polymer in an amount of mg. to l g. per mole of silver halide.

5. A light-sensitive photographic material according to claim 4, wherein the emulsion layer contains the polymer comprising alkylene oxide units in an amount of 10 mg. to 10 g. per mole of silver halide.

6. A light-sensitive photographic material according to claim 2, wherein the emulsion layer contains a N-vinyl-2 -pyrrolidone polymer having a molecular weight between 300 and 90,000.

7. A light-sensitive photographic material according to claim 3, wherein the polymer containing alkylene oxide units has a molecular weight of at least 1,500.

8. Process for developing an exposed direct positive silver halide photographic material comprising contacting a direct positive overall prefogged silver chloride emulsion containing less than one percent iodine with a polymer of N-vinyl-Z-pyrrolidone and developing.

9. The process according to claim 8 wherein the said photographic material contains an emulsion layer of the lith type.

10. The process according to claim 8, wherein the developing is lith developing.

11. The process according to claim 8, wherein the N-vinyl- 2-pyrrolidone polymer has been incorporated in a direct-positive silver halide emulsion layer of said material.

12. The process according to claim 8, wherein the developing is carried out in the presence of a polymer that contains alkylene oxide units.

13. The process according to claim 12, wherein the developing is carried out with a polymer that contains alkylene oxide units in the developing solution 14. The process according to claim 8, wherein the N-vinyl- 2-pyrrolidone polymer has a molecular weight of from about 300 and 90,000.

15. The process according to claim 11, wherein the N-vinyl- 2-pyrrolidone polymer is incorporated in the emulsion layer in an amount of from about 10 mg. to 14 g. per mole of silver halide or is incroporated in the developing solution in an amount of 10 mg. to 10 g. per litre. 

2. A light-sensitive photographic material according to claim 1, wherein the emulsion layer is a direct positive silver halide emulsion layer of the lith-type.
 3. A light-sensitive photographic material according to claim 1, wherein the emulsion layer contains a polymer containing alkylene oxide units.
 4. A light-sensitive photographic material according to claim 2, wherein the emulsion layer contains the N-vinyl-2 -pyrrolidone polymer in an amount of 10 mg. to 1 g. per mole of silver halide.
 5. A light-sensitive photographic material according to claim 4, wherein the emulsion layer contains the polymer comprising alkylene oxide units in an amount of 10 mg. to 10 g. per mole of silver halide.
 6. A light-sensitive photographic material according to claim 2, wherein the emulsion layer contains a N-vinyl-2 -pyrrolidone polymer having a molecular weight between 300 and 90,000.
 7. A light-sensitive photographic material according to claim 3, wherein the polymer containing alkylene oxide units has a molecular weight of at least 1,500.
 8. Process for developing an exposed direct positive silver halide photographic material comprising contacting a direct positive overall prefogged silver chloride emulsion containing less than one percent iodine with a polymer of N-vinyl-2-pyrrolidone and developing.
 9. The process according to claim 8 wherein the said photographic material contains an emulsion layer of the lith type.
 10. The process according to claim 8, wherein the developing is lith developing.
 11. The process according to claim 8 wherein the N-vinyl-2-pyrrolidone polymer has been incorporated in a direct-positive silver halide emulsion layer of said material.
 12. The process according to claim 8 wherein the developing is carried out in the presence of a polymer that contains alkylene oxide units.
 13. The process according to claim 12 wherein the developing is carried out with a polymer that contains alkylene oxide units in the developing solution.
 14. The process according to claim 8 wherein the N-vinyl-2-pyrrolidone polymer has a molecular weight of from about 300 and 90,000.
 15. The process according to claim 11 wherein the N-vinyl-2-pyrrolidone polymer is incorporated in the emulsion layer in an amount of from about 10 mg. to 14 g. per mole of silver halide or is incorporated in the developing solution in an amount of 10 mg. to 10 g. per liter. 